Apparatus for verifying hermeticity of small electronic assemblies

ABSTRACT

A sealed package in a test chamber is exposed to the flow of a high purity inert carrier gas at a lower than atmospheric pressure. If the sealed package leaks, the carrier gas purity level changes and is measured by a gas chromatograph detector. Buffer chambers surrounding the test chamber are continuously purged of any contaminants for preventing contamination of the test chamber from outside sources.

United States Patent Cramp et al.

[ 1 June 27, 1972 APPARATUS FOR VERIFYING HERMETI CITY OF SMALLELECTRONIC ASSEMBLIES Allen R. Cramp, Laguna Beach; Kenneth J. Brion,Fullerton, both of Calif.

North American Rockwell Corportion Jan. 4,197]

Inventors:

Assignee:

Filed:

Appl. No.:

U.S. Cl ..73/40.7

Int. Cl ..G01m 3/02, GOlm 3/20 Field of Search ..73/52, 40, 40.7, 38,49.2, 73/493 [56] References Cited UNITED STATES PATENTS 3,572,0963/1971 Meyer ..73/40.7 3,186,214 6/1965 Roberts ..73/40.7

Primary Examiner-Louis R. Prince Assistant Examiner-William A. Henry, I]

Att0rneyL. Lee l-lumphries, H. Fredrick Hamann and Robert G. Rogers [57]ABSTRACT A sealed package in a test chamber is exposed to the flow of ahigh purity inert carrier gas at a lower than atmospheric pressure. Ifthe sealed package leaks, the carrier gas purity level changes and ismeasured by a gas chromatograph detector. Buffer chambers surroundingthe test chamber are continuously purged of any contaminants forpreventing contamination of the test chamber from outside sources.

10 Claims, 3 Drawing Figures P'A'TENTEDJunN I972 I 3. 672 207 SHEET 10F2 FIG.I

INVENTORS ALLEN R. CRAMP BY KENNETH J. BRION MAW ATTORNEY PATENTEDJum m2sum z'ur 2 so 62b 6 Ill III III FIG. 2

TIME (SEWNDS) FIG. 3

APPARATUS FOR VERIFYING I-IERME'IICITY OF SMALL ELECTRONIC ASSEMBLIESBACKGROUND OF THE INVENTION l'll-ield of the Invention The inventionrelates to process and apparatus for verifying hermeticity of smallelectronic assemblies and more particularly to an improved leak testmethod wherein an inert carrier gas at lower than atmospheric pressureis passed over a test specimen and then to a detector where the carriergas purity is measured.

2. Description of Prior Art In general, leaks in hermetically sealeddevices fall into the categories of fine leaks (less than I X cc/sec stdatm) and gross leaks (greater than 1 X 10" cc/sec std atm). The mostcommon fine leak test method is a mass spectrometer detector instrumenttuned for helium. The test specimen is pressure impregnated with helium,which is used as the tracer gas, and then placed in a test cell which ispumped down to a hard vacuum. The detector instrument is sensitive tohelium leaking from the test specimen and is, in general, sensitive onlyto fine leaks. The sensitivity limit to large leaks is afunction ofvacuum pump down time and specimen internal volume. For a more detaileddescription, see U.S. Pat. No. 3,416,359 by H. A. Durbin et al whichissued on Dec. 17, 1968.

Patent application Ser. No. 785,879 by R. A. Meyer, filed Dec. 23, 1968,now U.S. Pat. No. 3,572,096, assigned to North American RockwellCorporation, and entitled Method and Apparatus for Inspecting SealedPackages for Leaks, discloses a method of and apparatus for inspectingsealed packages for leaks where a sealed package in an inspectionfixture is exposed to a carrier gas for a short time period that resultsin a readout developed by a detector instrument which distinguishesgross and fine package leaks. The Meyer inspection fixture has onebuffer or secondary chamber to prevent leakage into the test or primarychamber.

Althoughproviding a substantial improvement over prior leak detectors,the device of Meyer is believed to have low sensitivity and no easycalibration method. The lack of sensitivity is due partly to test cellpressure being higher than the internal pressure of the package. Formost leak testers, the test cell pressure and the internal pressure ofthe package mustequalize before the gas will diffuse from the package.

Further, the device of Meyer provides leak test data which is notcorrelatable with commonly used leak detection methods because it doesnot provide a definite pressure bias across the leak. In essence, themethod of Meyer measures diffusion rate across a hole rather than leakrate caused by pres.- sure differential. Allowable leak rates arecharacteristically specified as a rate resulting from a given pressuredrop across the leak. The units are cc/sec std atm. for the particulargas.

SUMMARY OF THE INVENTION Briefly, the test cell comprises a test chamberfor a hermetically sealed device and at least one buffer chamber aroundthe test chamber. An inert gas continuously purges the butter chamber toprevent contamination of the test chamber from external sources and toverify the seal of the test chamber.

A gas source provides an inert non-radioactive gas at a reduced pressurethrough the rest chamber for pulling impurities from the sealed device.The gas is at a pressure less than atmospheric and less than thepressure inside the sealed device. An impurity detectoris provided formeasuring any impurities in the gas from the test chamber.

In the preferred embodiment a moisture and cryogenic gas preparationmeans is provided to dry and clean the gas. Control valves and otherfluid flow and pressure regulatory elements are also included. Inaddition, a plurality of bufier chambers are included for providing testchamber isolation using a flow of buffer gas at preselected pressures toform pressure barriers and to continuously purge or flush the bufferchambers during the test.

In operation, a test specimen is placed in the test chamber, theresidual atmosphere gas is purged from the test chamber by a sweep gaswhile a carrier gas is being routed directly to the detector where thegas contamination level is measured. The carrier gas is then routedthrough the test chamber to flow around the test specimen which may bean electronic assembly. A lower purity level of the carrier gas detectedby the detector indicates the presence of a leak in the test specimen.

During the test, the buffer chambers are continuously purged with aninert gas at preselected pressures to establish a barrier around thetest chamber to preclude the leakage of ambient gas into the testchamber. One or more of the buffer chambers can be adapted to monitorthe gas flowing therein. As a result, the test cell seal can be checkedand detector indications verified.

The configuration of the test cell can be modified to allow for frequentcalibration of the system. The invention also provides data that iscorrelatable -with commonly used leak test methods.

It is therefore an object of the present invention to provide animproved process and apparatus for verifying the hermeticity of sealeddevices.

It is another object of the present invention to provide a process andapparatus for improving the sensitivity of a leak tester by usingrelatively contaminant free inert gas at a pressure less than thepressure of the sealed device being tested.

It is another object of the present invention to provide an improvedprocess and apparatus for distinguishing gross, medium and fine packageleaks in one test.

It is another object of the present invention to provide an improvedprocess and apparatus for providing a leak detector with improvedsensitivity that allows for system calibration.

These and additional objects will become more apparent when taken inconjunction with the following description and drawings in which likecharacters indicate like parts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of theapparatus for verifying hermeticity of small electronic packagesemploying one form of the test cell FIG. 2 illustrates a modification ofthe test cell of FIG. I which can be used with the apparatus of theinvention.

FIG. 3 is a graphical representation of curves developed by the leakdetection process and apparatus of the invention when testing sealedpackages for the presence or absence of leaks.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, one form ofthe apparatus for verifying hermeticity of small electronic assembliesin accordance with the present invention includes a test cell 10 whichin the form as shown has separable mating elements 12 and 13 that arereleasably mated together by clamps or other appropriate means toprovide mutual fluid flow and pressure isolation of test chamber 11,bufier chambers 15 and 16 and the test cell ambient atmosphere.Resilient sealing members 14, which can be 0 rings or the like, arepositioned as shown and facilitate fluid flow and pressure isolation anddetermine the test chamber 48 and the buffer chambers 15 and 16.

In the apparatus of FIG. I, inert non-radioactive gas source 17 isconnected to regulator 35 which controls the flow of gas in line 36through moisture trap 18 and cryogenic gas cleaning trap 19 toregulators 30 and 31. The gas source is connected through regulator 30by means of valve 23 to test chamber 48.

The gas source 17 is also connected by regulator 31 through valve 22 totest chamber 48. In addition, the gas source 17 is connected throughregulator 31 by means of valve 21 to buffer chamber 15. Gas source 17 isalso connected by regulator 30 by means of valve 23 and 24 throughmoisture trap 27 to detector 29. Gas source 33 contains the same inertnon-radioactive gas as gas source 17 and is connected by regulator 34 tobuffer chamber 16.

Gas outlet lines 43, 44 and 45 are connected respectively to bufferchambers 16 and and to test chamber 48. Outlet gas from test chamber 48flows through line 45 and is either directed to detector 29 by valve 24or is exhausted into subambient pressure container 32 by means of valve25. Gas flowing through detector 29 is exhausted into sub-ambientpressure container 32 by means of valve 28. Outlet gas from bufferchamber 15 is exhausted into sub-ambient pressure container 32 by valve26. Gas from source 33 flowing into buffer chamber 16 by means of line42 is exhausted into the ambient atmosphere from buffer chamber 16 bymeans of line 43. It is obvious to one skilled in the art that gassources 33 and 17 may be combined. However, in the preferred embodimentin the present invention these gas sources are separated since it ismore important that gas flowing through buffer chamber 15 and throughtest chamber 48 be of high purity whereas the gas in gas source 33 maybe less pure since requirement for high purity gas in buffer chamber 16is not as important. Vacuum pump 20 exhausts gas from sub-ambientpressure container 32 into the ambient atmosphere through line 37. Acryogenic trap is provided to prevent back diffusion of pump oil vaporsinto container 32.

Proper operation of the present invention requires certain relativepressures to exist in certain areas. For instance, typical absolutepressures may be one psi in sub-ambient pressure container 32, six totwelve psi in test chamber 48, five psi in buffer chamber 15, eighteenpsi in bufier chamber 16, and sixty psi in line 39. It is therefore seenthat a leak between test chamber 48 and buffer chamber 15 would efiect aflow of gas from test chamber 48 to buffer chamber 15 and not viceversa. Likewise, a leak between buffer chamber 16 and the test cellambient atmosphere would effect a flow of gas from buffer chamber 16 tothe ambient atmosphere. Also, the presence of regulators 30 and 31, andvalves 21, 22, 23, 24, 25, and 28 within subambient pressure container32 will effect that any leaks in the aforementioned regulators or valveswould be from the regulators and/or valves into the sub-ambient pressuretank container 32. Therefore, the regulators and valves pertinent to thecarrier gas flowing through test chamber 48 and the buffer gas flowingthrough buffer chamber 15 are arranged so that any leaks in theregulators or valves would not contaminate the gas flowing through thetest cell. The sub-ambient pressure container 32 is therefore a pressurereference for the regulators supplying carrier gas to test chamber 48and buffer gas to buffer chamber 15 and is important in preventingcontamination of the test cell.

There are three gas functions in the system. The first is carrier gaswhich always flows to the detector 29 either through the test cell 48 orby means of bypass line 46. The second is sweep gas which is used onlyto flush residual atmospheric gas out of the test chamber 48 after thetest specimen 1 1 has been inserted. The third is buffer gas which isdirected to flow through the buffer chambers 15 and 16 and is used toestablish a barrier around the test cell to preclude the leakage ofatmospheric gas into the test cell. Moisture and cryogenic traps areprovided as shown for selective cleaning of the gas.

In operation, a test specimen 1 1 is first inserted into the testchamber 48 of test cell 10 and mating members 12 and 13 are mated toisolate the specimen 1 1 from the test cell ambient atmosphere.

After the test cell is closed, pressure regulators 35 and 31 areactuated and valve 22 is opened to allow the sweep gas to flush or purgethe residual atmosphere from the test chamber 48 with the gas beingexhausted into sub-ambient pressure container 32 by valve 25. At thesame time, pressure regulator 30 is actuated and valves 23 and 24 areopened to bypass the test cell and allow the carrier gas to flowdirectly to the detector 29 where the gas contamination level ismeasured. After a predetermined amount of time, valves 22, 23 and 24 are1 aimultaneously actuated to direct the carrier gas through the testchamber 48, to flow around the test specimen, and by means of line 45through valve 24 on to detector 29. A flower purity level of the carriergas after being passed around the test specimen is detected by thedetector and indicates the presence of a leak in the test specimen.

The test cell operating pressure controlled by gas regulator 30 isadjusted to a definite pressure level below the internal pressure of thetest specimen. Buffer gas pressure is adjusted by regulator 31 so thatthe inner buffer chamber 15 is below test cell pressure and by regulator34 so that the outer buffer chamber 16 is above atmospheric pressure.When the test cell 10 is open for loading of the test chamber withanother test specimen, appropriate regulators and valves are operated torestrain gas flow. For instance, valve 26 is closed to prevent loss ofsub-ambient pressure in the container 32 and valve 28 is closed toprevent flow from container 32 into detector 29.

During the test, the buffer chambers 15 and 16 are continuously purgedwith the inert gas from gas sources 17 and 33 to establish a barrieraround the test chamber 48 to preclude the leakage of ambient gas intothe test chamber. As can readily be seen, one or more of the bufferchambers of the present invention can be adapted by means of appropriatevalves to monitor the gas flowing therein and as a result, the test cellseal can be checked and detector indications verified.

The configuration of the test cell 10 can be modified to allow forfrequent calibration of the system. This calibration will then allow forcorrelation between the data produced by the detector and other commonlyused leak test methods. FIG. 2 illustrates a mechanical leak which is amodification of the test cell 10 of FIG. 1 which can be used with theapparatus of the present invention. More particularly, FIG. 2illustrates a modification of mating part 12 of test cell 10 wherein agas inlet 61 is provided such that drive screws a and 65b apply pressureto squeeze pistons 62a and 62b which in turn squeeze gas inlet tube 61.In operation, the mechanical leak 60 is mated to test cell member 13instead of mating member 12 to member 13. A contaminant gas typical ofwhat will be leaking from a leaky test specimen during leak testing ofthe test specimen is allowed to leak into the test chamber at acontrollable rate and pressure by means of adjustment of screws 63a and63b. A calibration curve is thus obtained wherein a known amount ofcontaminant is leaked into the test chamber. Therefore, a correspondingpoint on the calibration curve obtained during test of a specimen willindicate a contaminant leak corresponding in cc/second std atrn to themeasured leak allowed to pass through the mechanical leak during thecalibration procedure. The calibration procedure thus also allows forcomparison of the test results of the present invention to commonly usedleak test methods where the rest results are in units of cc/second stdatm.

The detector 29 is a gas chromatograph wherein the inert gas moleculesare bombarded in a tritium cell, the tritium knocking an electron of theinert gas to an outer ring of the inert gas thus effecting a metastablestate. The inert gas then readily collapses to its normal state, givingup energy in the form of a photon to the leaked contaminating gas, suchas N 0 CO etc. thereby ionizing the contaminating gas. The ionized gasis then attracted to a plate of the tritium cell providing acalibratable signal. Therefore, in essence, the detector monitors thepurity of the inert gas. If the test specimen leaks, the level of inertgas purity changes and can be measured.

Referring to FIG. 3, there is presented a graphical representation ofcurves developed by the leak detection process and apparatus of thepresent invention for testing sealed test specimens for the presence orabsence of leaks. Curve is a detector trace indicative of no leak in thetest specimen. Curve 71 is indicative of a fine leak with curves 72 and73 indicative of gross leaks. Dotted curve 74 presents a trace normallytypical of the early part of a detector leak signal wherein the valveand regulator arrangement of the invention is not optimized to provideminimum dead volume and adequate port to port seal. The regulator andvalve arrangement of the present invention as shown in FIG. 1, hassignificantly im proved the characteristic output signal shown by curve74 so that the signal, even during the first few seconds, is as shown bythe solid curves and is on scale and usable. The result is that readoutproblems and test times are considerable reduced.

While there has been shown what is considered to be preferredembodiments of the present invention, it will be manifest that manychanges and modifications may be made therein without departing from theessential spirit of the invention. It is intended, therefore, in theannexed claims, to cover all such changes and modifications as may fallwithin the true scope of the invention.

We claim:

1. Apparatus for detection of leaks in sealed devices comprising,

a test chamber for a sealed device;

means for isolating said test chamber from the ambient atmosphere;

at least one gas source providing a supply of carrier gas atpredetermined pressures;

means for providing a flow of said carrier gas from said supply throughsaid test chamber and around said sealed device;

detector means for detecting impurities contributed to said carrier gasby said sealed device;

means for routing said carrier gas from said test chamber to said meansfor detecting impurities; and

a sub-ambient pressure reference container enclosing at least said meansfor routing said carrier gas to said detector means.

2. The invention according to claim 1 and further comprisa plurality ofbuffer chambers for isolating said test chamber from the ambientatmosphere;

each of said buffer chambers positioned whereby each succeeding one ofsaid buffer chambers surrounds each preceding one of said bufferchambers to provide fluid flow and pressure isolation of said testchamber and said buffer chambers each from the ambient atmosphere andfrom each other; and

said test chamber and each of said buffer chambers having inlet andoutlet means for passing gas through said chambers.

3. The invention according to claim 2 and further comprising,

means for providing said carrier gas to said test chamber and saidbuffer chambers at selected relative pressures; said pressures selectedto provide pressure barriers to leaks into said test chamber. 4. Theinvention according to claim 1 wherein said gas source furthercomprises,

control valve means for providing a sweep gas at a preselected pressureto purge residual atmosphere from said test chamber prior to testingsaid sealed device;

control valve means for continuously purging said buffer chambers withbuffer gases at preselected relative pressures during test of saidsealed device;

said bufler gases having relative pressures to cause a leak between saidtest chamber and said buffer chambers to effect a flow of gas from saidtest chamber;

control valve means for providing said carrier gas at a preselectedpressure to said test chamber during test of said sealed device; and

said carrier gas being further routed to said detector where theimpurity level of said carrier gas is measured by said detector whereinsaid impurity level indicates the presence or absence of a leak in saidsealed device.

5. The invention according to claim 4 wherein the respective pressuresof said buffer gases flowing through said bufier chambers relative toeach other, to said test chamber and to the ambient atmosphere of saidtest cell are selected to minimize leaks through said buffer chambersbetween the ambient atmosphere and said test chamber.

6. The invention according to claim 4 wherein the gas flowing through atleastone of said buffer chambers is monitored to provide a self check ofthe isolation of said test cell from ambient atmosphere and to verifydetector indications.

7. Apparatus for detecting leaks in sealed devices comprising,

a test cell containing an inner test chamber adapted to receive sealeddevice and to isolate it from ambient atmosphere;

at least one gas source providing a supply of gas at predeterminedpressures;

detector means for analyzing the purity of said gas;

control valve and other fluid flow and pressure regulating elementsconnecting said test cell, said detector and said gas sources to providethat a carrier gas at preselected pressure flows around said testspecimen through said test cell and to said detector, said detectoranalyzing the purity level of said gas passing through said test celland detecting the impurity exuding from a leak in said sealed device;and

said control valve and other fluid flow and pressure regulating elementsinclude a vacuum providing device and a sub-ambient pressure referencecontainer that encloses at least said control valve elements routingsaid carrier gas to said detector.

8. Apparatus for detecting leaks in hermetically sealed devicescomprising,

a test cell with an inner test chamber adapted to provide a receptaclefor a hermetically sealed device and to isolate it from ambientatmosphere;

at least one buffer chamber wherein the innermost of said bufierchambers isolates said test chamber from test cell ambient atmosphere;

each of said buffer chambers positioned whereby each succeeding one ofsaid buffer chambers surrounds each preceding one of said bufierchambers to provide fluid flow and pressure isolation of said testchamber and said buffer chambers each from the test cell ambientatmosphere and from each other;

at least one gas source providing a supply of an inert nonradioactivegas at predetermined pressures;

said test chamber and each of said buffer chambers having inlet andoutlet means for passing gas through said chambers;

gas chromatograph detector means insensitive to said inertnon-radioactive gas but sensitive to said impurities in said gas foranalyzing the purity of said gas;

control valve and other fluid flow and pressure regulating elementsconnecting said test cell and said gas sources so that said gas flowsaround said test specimen through said test cell and connecting saidtest cell and said detector so that said detector analyzes the puritylevel of said gas passing through said test cell and detects only theimpurity exuding from a leak in said hermetically sealed device; and

said control valve and other fluid flow and pressure regulating elementsinclude moisture and cryogenic traps, a vacuum providing device, and asub-ambient pressure reference container enclosing at least the valvesrouting said inert non-radioactive gas to said detector.

9. The invention of claim 8 in which said gas source further provides,

means for providing a sweep gas to purge residual atmosphere from saidtest chamber prior at test of said hermetically sealed device;

means for providing buffer gases at preselected pressures to formpressure barriers and to purge said buffer chambers continuously duringtest of said hermetically sealed device;

means for providing a carrier gas at reduced pressure to said testchamber during test of said hermetically sealed device with said carriergas routed through said test chamber to flow around said sealed device;and

said carrier gas being further routed to a detector where the impuritylevel of said carrier gas is measured by said detector wherein saidimpurity level indicates the presence or absence of a leak in saidhermetically sealed device.

10. The invention according to claim 8 wherein said apparatus fordetecting leaks further comprises,

means for providing calibration of said apparatus so that results arecorrelatable with other leak testers wherein leaks are rated in unitssuch as cc/sec std atm.

1. Apparatus for detection of leaks in sealed devices comprising, a test chamber for a sealed device; means for isolating said test chamber from the ambient atmosphere; at least one gas source providing a supply of carrier gas at predetermined pressures; means for providing a flow of said carrier gas from said supply through said test chamber and around said sealed device; detector means for detecting impurities contributed to said carrier gas by said sealed device; means for routing said carrier gas from said test chamber to said means for detecting impurities; and a sub-ambient pressure reference container enclosing at least said means for routing said carrier gas to said detector means.
 2. The invention according to claim 1 and further comprising, a plurality of buffer chambers for isolating said test chamber from the ambient atmosphere; each of said buffer chambers positioned whereby each succeeding one of said buffer chambers surrounds each preceding one of said buffer chambers to provide fluid flow and pressure isolation of said test chamber and said buffer chambers each from the ambient atmosphere and from each other; and said test chamber and each of said buffer chambers having inlet and outlet means for passing gas through said chambers.
 3. The invention according to claim 2 and further comprising, means for providing said carrier gas to said test chamber and said buffer chambers at selected relative pressures; said pressures selected to provide pressure barriers to leaks into said test chamber.
 4. The invention according to claim 1 wherein said gas source further comprises, control valve means for providing a sweep gas at a preselected pressure to pUrge residual atmosphere from said test chamber prior to testing said sealed device; control valve means for continuously purging said buffer chambers with buffer gases at preselected relative pressures during test of said sealed device; said buffer gases having relative pressures to cause a leak between said test chamber and said buffer chambers to effect a flow of gas from said test chamber; control valve means for providing said carrier gas at a preselected pressure to said test chamber during test of said sealed device; and said carrier gas being further routed to said detector where the impurity level of said carrier gas is measured by said detector wherein said impurity level indicates the presence or absence of a leak in said sealed device.
 5. The invention according to claim 4 wherein the respective pressures of said buffer gases flowing through said buffer chambers relative to each other, to said test chamber and to the ambient atmosphere of said test cell are selected to minimize leaks through said buffer chambers between the ambient atmosphere and said test chamber.
 6. The invention according to claim 4 wherein the gas flowing through at least one of said buffer chambers is monitored to provide a self check of the isolation of said test cell from ambient atmosphere and to verify detector indications.
 7. Apparatus for detecting leaks in sealed devices comprising, a test cell containing an inner test chamber adapted to receive sealed device and to isolate it from ambient atmosphere; at least one gas source providing a supply of gas at predetermined pressures; detector means for analyzing the purity of said gas; control valve and other fluid flow and pressure regulating elements connecting said test cell, said detector and said gas sources to provide that a carrier gas at preselected pressure flows around said test specimen through said test cell and to said detector, said detector analyzing the purity level of said gas passing through said test cell and detecting the impurity exuding from a leak in said sealed device; and said control valve and other fluid flow and pressure regulating elements include a vacuum providing device and a sub-ambient pressure reference container that encloses at least said control valve elements routing said carrier gas to said detector.
 8. Apparatus for detecting leaks in hermetically sealed devices comprising, a test cell with an inner test chamber adapted to provide a receptacle for a hermetically sealed device and to isolate it from ambient atmosphere; at least one buffer chamber wherein the innermost of said buffer chambers isolates said test chamber from test cell ambient atmosphere; each of said buffer chambers positioned whereby each succeeding one of said buffer chambers surrounds each preceding one of said buffer chambers to provide fluid flow and pressure isolation of said test chamber and said buffer chambers each from the test cell ambient atmosphere and from each other; at least one gas source providing a supply of an inert non-radioactive gas at predetermined pressures; said test chamber and each of said buffer chambers having inlet and outlet means for passing gas through said chambers; gas chromatograph detector means insensitive to said inert non-radioactive gas but sensitive to said impurities in said gas for analyzing the purity of said gas; control valve and other fluid flow and pressure regulating elements connecting said test cell and said gas sources so that said gas flows around said test specimen through said test cell and connecting said test cell and said detector so that said detector analyzes the purity level of said gas passing through said test cell and detects only the impurity exuding from a leak in said hermetically sealed device; and said control valve and other fluid flow and pressure regulating elements include moisture and cryogenic traps, a vacuum providing device, and a sub-ambient pressure reference coNtainer enclosing at least the valves routing said inert non-radioactive gas to said detector.
 9. The invention of claim 8 in which said gas source further provides, means for providing a sweep gas to purge residual atmosphere from said test chamber prior at test of said hermetically sealed device; means for providing buffer gases at preselected pressures to form pressure barriers and to purge said buffer chambers continuously during test of said hermetically sealed device; means for providing a carrier gas at reduced pressure to said test chamber during test of said hermetically sealed device with said carrier gas routed through said test chamber to flow around said sealed device; and said carrier gas being further routed to a detector where the impurity level of said carrier gas is measured by said detector wherein said impurity level indicates the presence or absence of a leak in said hermetically sealed device.
 10. The invention according to claim 8 wherein said apparatus for detecting leaks further comprises, means for providing calibration of said apparatus so that results are correlatable with other leak testers wherein leaks are rated in units such as cc/sec - std atm. 